This invention relates to disk-type wood chippers for cutting uniform chips from a log. The invention is more particularly directed to an improved segmental knife holder which supports removable knife blade assemblies on a front face of the chipper disk. The invention is more specifically concerned with a knife holder that has a replaceable wear surface on the side that faces logs being fed into the chipper.
A typical rotary disk type chipper is described in detail in U.S. Pat. No. 4,784,337. In the chipper of this configuration, logs are fed against a rotating disk which carries a number of radially disposed knives clamped between a main portion of the disk and respective segmental or pie-wedge shaped knife holders. In these chippers, the knife holders extend up to a chip slot associated with a successive knife assembly from the knife assembly that it is responsible for clamping. The proximal surface of the knife holder is typically given a hardening treatment, i.e. coated with a hardfacing substance harder than the mild steel of which it is constructed, so that it can endure continuous abrasion from the incoming logs. However, after a period of use, the hardfacing coating on the knife holders will wear or abrade away. This causes portions of the mild steel beneath it to become exposed, and this significantly reduces the efficiency of the chipper. Therefore, the hardface coating on the knife holders must be repaired periodically or the knife holders must be entirely replaced.
The proximal or log-facing surface of the knife holder has a rather complex twisted geometry, that is, it is helicoid rather than flat. This characteristic makes machining of the worn knife holders rather difficult when repair of the hardcoating surface treatment is required.
In the conventional wood chipper, the knife holder is in the form of a one-piece segment with a helicoid surface treated with a hardfacing. When the hardfacing on the helicoid surface wears through, the worn surfaces are welded flush with the hardfacing, and then the entire face is rehardfaced. Additional welding and machining on the back or distal surface of the knife holder segment may be required to bring the thickness of the knife holder back into proper tolerance. In addition, with each successive repair to the segmental knife holder, the geometrical helicoid surface and the hardfacing surface finish each degrade, causing a reduction in the quality of wood chips produced.
For these reasons, it was desired to provide an improved segmental knife holder which avoids these problems and which facilitates knife holder repair without at the same time bringing on new problems such as degradation of wood chip quality.